Electronic – Problem with the 74160 decade counter

digital-logic

I am experimenting with different TTL components and am having a lot of trouble with the 74160 decade counter. I don't know if it's my inexperience or if I'm dealing with a malfunctioning IC, but the IC isn't doing what it's supposed to, and it heats up pretty darn fast (I always check for heating once I power up)

After some testing, I noted that all I have to do is connect the GND to ground and the +5V pin to 5V and it starts heating up fast. If I add a resistor connecting to ground, it doesn't heat up, but it heats up once I connect the remaining pins (as it stands, pins 7 and 8 are grounded, 9 and 16 are in +5). As soon as I power it up, all the outpins turn HIGH.

So here is what I'm wondering:

Do I ever need a resistor once a TTL datasheet tells me to connect such and such pins to ground or to +5V or can I connect them directly?
Can I conclude that my 74160 is short-circuited/malfunctioning?
Is there anything else I might be doing wrong?

Best Answer

After looking at the datasheet, the part normally pulls 60-70mA at 5V, dissipates 350mW. This will be warm to the touch, not hot. Not sure why you're using an old TTL device, newer fast CMOS parts have standby currents in the 100uA range.

You mention adding a resistor to gnd, what's the other end of the resistor connected to?

You may float TTL inputs, hopefully there are no DC loads on the outputs, otherwise the chip will draw current unnecessarily.

Try this: connect a series resistor (5 ohms) inline with Vcc. If you get a voltage drop > 0.5V across the resistor, then either the chip is damaged or the outputs (including RCO) are driving heavy loads.

Related Solutions

Electronic – How does the 4017B Decade Counter work

Correct, those are normal D flip-flops. The 4017B itself is just some D flip-flops behind a decoder, so just flip-flops wouldn't be enough to replicate the whole counter; you can use a 74xx42 or 74xx45 as the decoder after the flip-flops.

Realisation of asynchronous decade counter

An asynchronous counter means that the states of flip flops dont change simultaneously. This is evident by the fact that all flip flops are clocked by different clocks rather than a single master clock.

As far as working is concerned, a timing diagram may help :

enter image description here

1) First flip flop (Q0) changes state on PGT of the clock.

2) Second flip flop changes state on the PGT of its clock. Since it is clocked by Q0, it will change states when corresponding transition occurs for Q0 rather that Clock.

....and so on for subsequent flip flops.

Why are J and K inputs always 1 ?

The flip flops need to toggle on the occurance of PGT. Since a J-K flip flop toggles only when both inputs are HIGH or 1 ( also called toggle mode of operation), hence they must be kept high.

How does CLR reset these flip-flops ?

If you look carefully at 'your' circuit, the input of the Nand gate is connected to the 2nd and 4th flip flops. The output of Nand gate is low only when both the inputs are HIGH. Plus you have active Low reset. So whenever the 2nd and 4th flip flops go HIGH for the first time simultaneously, which happens for binary 1010 or decimal 10, the flip flops will all reset and recycle to initial state ie 0000. Typically this is used to create counters which count less than the maximum no of available states. In your case, 4 flip flops should have counted till 1111 or decimal 15. However, presence of Nand terminates the count early.

Best Answer

Related Solutions

Electronic – How does the 4017B Decade Counter work

Realisation of asynchronous decade counter

Related Topic